I have aloud vacuum noise coming from the engine when I start it,any ideas

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I hear aloud vacuum noise coming from the engine on start up and it doesn't want to idle; after you hold it at a high idle it will stop making the noise, it will then idle rough or idle high; I have replaced the idle air control,the throttle positioning sensor and the throttle body gasket, can you think of anything else I can check. What seems to make the problem better or worse? It doesn't it every time I start it How long have you had this problem? Months